P1 4.2.3 Plant tissues, organs and systems (will come up) Flashcards
Order of tissues on a leaf (top to bottom)
Waxy cuticle Upper epidermis Palisade mesophyll Spongy mesophyll Xylem and phloem Guard cells surrounding stomata Lower epidermis
How the structure of epidermal tissue is related to its function
The epidermal tissue is covered with a waxy cuticle which help to reduce water loss by evaporation
How the structure of the upper epidermis is related to its function
It’s transparent so that light can pass through it to the palisade layer
How the structure of palisade tissue is related to its function
It has lots of chloroplasts. This means they are near the top of the leaf where they can get the most light
How are the tissues of leaves adapted for gas exchange
The lower epidermis is full of stomata which let CO2 diffuse directly into the leaf
Guard cells open and close these in response to the environment
The air spaces in spongey mesophyll tissue increase the rate of diffusion of gases
How does light intensity affect transpiration rate
The brighter the light the greater the transpiration rate
Stomata begin to close when it gets darker as photosynthesis can’t happen in the dark, so CO2 doesn’t need to be let in
Very little water can escape when stomata are closed
How does temperature affect transpiration rate
The higher the temp. the faster transpiration happens
When its warm, water particles have more energy to evaporate and diffuse out of the stomata
How does air flow affect transpiration rate
The better the air flow the greater the transpiration rate
If there is good air flow, the water vapour is swept away keeping a low concentration of water in the air outside the leaf so diffusion happens quickly
Other way around for bad air flow
How does humidity affect transpiration rate
The drier the air around a leaf, the faster transpiration happens
Similar to air flow - if air is humid there is a lot of water in it already so not much of a difference between inside and outside the leaf meaning slower diffusion
What is a plant organ system made up of and what does it do
Roots, stems and leaves
For transport of substances around the plant.
What is translocation and where does it happen
The movement of dissolved sugars around a plant
Phloem
What is a transpiration stream and where does it happen
in detail steps
The movement of water from a plants roots through the xylem and out the leaves
- Water from inside a leaf evaporates and diffuses out of the leaf mainly through stomata
- Creates a slight shortage of water in the leaf so more water is drawn up from the rest of the plant through the xylem vessels to replace it
- This in turn means more water is drawn up from the roots and so there’s a constant transpiration stream of water through the plant
Structure of xylem
It is composed of hollow tubes strengthened by lignin adapted for the transport of water in the transpiration stream.
What is the role of the stomata and guard cells
To control gas exchange and water loss
What happens between the stomata and guard cells when the plant has lots of water
The guard cells fill with water and go plump and turgid. This makes the stomata open so gases can be exchanged for photosynthesis
